Anti-CD200R1 antibody promoted T-cell receptor-driven proliferation of CD4+ T cells in systemic lupus erythematosus patients. (A) In systemic lupus erythematosus (SLE) patients and healthy controls (HCs), no significant difference in proliferation of anti-CD3/CD28-stimulated CD4+ T cells was found in the presence of CD200Fc or IgG control. (B) In SLE patients, anti-CD200R1 promoted anti-CD3/CD28-stimulated proliferation of CD4+ T cells in a concentration-dependent manner, whereas this was not observed in HCs. Fluorescence-activated cell sorting (OK)plots are representative of five experiments performed on five SLE patients and HCs, respectively. CFSE, carboxyfluorescein diacetate succinimidyl ester.